This application claims the priority benefit of Japanese application Ser. No. 2000-181353, filed Jun. 16, 2000.
1. Field of Invention
This invention relates to a propylene series resin sheet that has high frequency welding characteristics obtained from a mixture of a specific polypropylene series composition and a specific ethylene series copolymer. More particularly, this invention relates to a propylene series resin sheet that has high frequency welding characteristics, excellent transparency, low-temperature impact resistance, and surface durability.
2. Description of Related Art
Polypropylene sheets are widely used as materials for wrapping and for decoration, because polypropylene sheets have excellent mechanical, optical and thermal properties suitable for wrapping.
As for polypropylene, the propylene-ethylene block copolymers, consisting of propylene homopolymer, propylene-xcex1-olefin di-copolymer or propylene-xcex1-olefin multi-copolymer, propylene homopolymer/propylene-ethylene copolymer, are used. The features of the aforementioned compositions are suitable for the above-mentioned usage.
However, it is difficult to treat the conventional polypropylene sheet with the high frequency welding process, thus limiting its usage. Furthermore, methods for improving the properties of transparency, low-temperature impact resistance and surface durability are in conflict with one another. For example, a polypropylene sheet using propylene homopolymer has inferior low-temperature impact resistance. A polypropylene sheet using a propylene-xcex1-olefin di-copolymer or propylene-xcex1-olefin multi-copolymer has good transparency, but has inferior low-temperature impact resistance and surface durability. On the other hand, a polypropylene sheet using a propylene-ethylene block copolymer, which fails to reach a specific intrinsic viscosity ratio, has excellent low-temperature impact resistance, but has inferior transparency and surface durability, further causing fish-eyed defects.
In the conventional polypropylene sheets, it is impossible to achieve transparency, low-temperature impact resistance and surface durability together with high frequency welding characteristics.
The invention provides a propylene series resin sheet having transparency, low-temperature impact resistance and surface durability together with high frequency welding characteristics.
In order to achieve the previous purposes, this invention solves the prior art problems and provides a propylene series resin sheet having transparency, low-temperature impact resistance and surface durability together with high frequency welding characteristics.
The polypropylene series composition consists of a crystalline polypropylene component (PP) and propylene-xcex1-olefin copolymer component (RC, with xcex1-olefin other than propylene). The propylene-xcex1-olefin copolymer component (RC) has an intrinsic viscosity [xcex7]RC below 6.5 dl/g. The viscosity ratio [xcex7]RC/[xcex7]PP of the intrinsic viscosity [xcex7]RC and the intrinsic viscosity [xcex7]PP of the crystalline polypropylene component (PP) is about 0.6xcx9c1.2. The weight of the crystalline polypropylene component (PP) is represented as WPP, while the weight of the propylene-xcex1-olefin copolymer component (RC) is represented as WRC. The multiplying product of the weight ratio WPP/WRC and the viscosity ratio [xcex7]RC/[xcex7]PP ([xcex7]RC/[xcex7]PP)xc3x97(WPP/WRC) is in a range between 0.2 to 4.5 for the polypropylene series composition. By using the RC that contains discrete domains distributed along the flowing directions of the PP during molding or distributed randomly but at least connected to another domain, the sheets obtained have excellent transparency, low-temperature impact resistance and surface durability. Furthermore, a specific ethylene series copolymer with a large dielectric loss tangent (tan xcex4) is mixed into the polypropylene series composition, thus increasing high frequency welding characteristics and obtaining a propylene series resin sheet with excellent transparency, low-temperature impact resistance and surface durability at the same time.
As described above, the present invention provides a sheet that has high frequency welding characteristics, excellent transparency, low-temperature impact resistance, and surface durability. Moreover, the present invention provides a propylene series resin sheet having high frequency welding characteristics and the aforementioned features that is suitable for various applications, for example sheets for stationery and as a construction material used in a porch.
The present invention has the following compositions:
(1) A propylene series resin sheet characterized by a mixture of a polypropylene series composition with a weight percentage of 50-99% and an ethylene series copolymer with a weight percentage of 1-50%. The aforementioned polypropylene series composition consists of a crystalline polypropylene component (PP) and a propylene-xcex1-olefin copolymer component (RC, with any xcex1-olefin other than propylene). The propylene-xcex1-olefin copolymer component (RC) has an intrinsic viscosity [xcex7]RC of 6.5 dl/g or less. The viscosity ratio [xcex7]RC/[xcex7]PP of the intrinsic viscosity [xcex7]RC and the intrinsic viscosity [xcex7]PP of the PP is about 0.6xcx9c1.2. The weight of the PP is represented as WPP, while the weight of the RC is represented as WRC. The multiplying product of the weight ratio WPP/WRC and the viscosity ratio [xcex7]RC/[xcex7]PP [([xcex7]RC/[xcex7]PP)xc3x97(WPP/WRC) is in a range between 0.2 to 4.5 for the polypropylene series composition. The aforementioned ethylene series copolymer has a peak value of a dielectric loss tangent larger than 5.0xc3x9710xe2x88x923 (100 kHz) under a cohesive energy density of 60-90 cal/cm3.
(2) In the propylene series resin sheet as cited above in (1), the aforementioned polypropylene series composition consists of crystalline polypropylene component (PP) that contains propylene-xcex1-olefin copolymer with a propylene content of 90% more by weight and propylene-xcex1-olefin copolymer component (RC).
(3) The propylene series resin sheet as cited above in (1), the polypropylene series composition consists of a crystalline polypropylene component (PP) and a propylene-xcex1-olefin copolymer component (RC) that contains a propylene-xcex1-olefin copolymer (an xcex1-olefin other than propylene) with an xcex1-olefin content of 10-60% by weight.
(4) In the propylene series resin sheet as cited above in (1), the polypropylene series composition consists of a crystalline polypropylene component (PP) and a propylene-xcex1-olefin copolymer component (RC) that contains a propylene-ethylene copolymer with an ethylene content of 15-60% by weight.
(5) In the propylene series resin sheet as cited above in (1), the ethylene series copolymer includes copolymers of ethylene with unsaturated carboxylic acid, its derivatives or vinyl ester.
(6) In the propylene series resin sheet as cited above in (1), the ethylene series copolymer includes copolymers of ethylene with unsaturated carboxylic acid or its derivatives.
(7) A propylene series resin, multi-layered sheet includes at least a layer of the propylene series resin sheet as cited above in (1) to (6).
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.